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I am working on a small waste treatment project where there is a small mixing vessel (about 5 liters - more or less 20cm diameter). The mixing process produces methane gas which shouldn't escape the confines of the mixing vessel (odor and flammability).

Some other salient parameters (as I perceive them):

  • The shaft diameter is small (about 16mm).
  • the shaft rotates really slow (about 10-30 rpm).
  • the pressure of the gas is low (just over 1Atm ).

I was wondering whether what type of seal would be most appropriate for this type of application. My first instinct was a lip sea with a garter spring. I know there are other types of seals (e.g. packing, mechanical seals, tandem, cartridge), but I have little to no experience with most of them.

The cost would be a primary driver in this application, so any indication about the *cost effectiveness * would be welcome. For example, I have seen some of gas seals used in the petroleum industry but the cost is prohibitive.

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Nitrile rubber (Buna-N) o-ring seals would be the most cost effective choice for your application. This is a valuable resource on o-ring seal design, for your case a dynamic rotary seal.

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Have you considered enclosing that mixing vessel entirely then you only have pipe in and pipe out and an electrical connection.

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  • $\begingroup$ Hi, thanks for the input. One of the reason that I'm looking for a gas seal is that there was a worry of an electrically induced fire if the flammable gas gets out. So the idea is to keep the electrical motors and the gas separate. $\endgroup$
    – NMech
    Dec 20 '20 at 19:34
  • $\begingroup$ @NMech so if there is no oxygen then the methane won’t burn... $\endgroup$
    – Solar Mike
    Dec 20 '20 at 19:38
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    $\begingroup$ I thought of that but at first glance it seems as a gamble. E.g what happens if you need to make some repairs and you open the outer box and there is gas trapped inside. Additionally i dont know the ratio of air/methane that is required for sustained combustion, so i dont want to leave that to chance. $\endgroup$
    – NMech
    Dec 20 '20 at 19:48

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